1. Field of the Invention
The present invention relates to a semiconductor device and a method of operating the same, and more particularly, to a cross-point latch, a method of latching of a logic value and methods of restoration and inversion of signal using the cross-point latch.
2. Description of the Related Art
Digital circuits comprise combinational circuits and sequential circuits. A combinational circuit has no memory and is a circuit in which an output is determined by an input. However, a sequential circuit is a circuit in which an output is determined by both an input and a state value (which is determined by inputs in the past) stored in the circuit. A sequential circuit has a memory device in the circuit for storing values. The memory device is called a flip-flop device. The flip-flop device can store information of 1 bit (0 or 1), and can be configured to various ways according to methods of connecting logic gates.
A latch is an example of the flip-flop device. In order to increase integration density of the latch, a molecule cross-bar latch has been disclosed, for example, in Korean patent publication No. 10-2005-0040829.
The molecule cross-bar latch has advantages in increasing the integration density, however, has the following disadvantages.
First, a molecule switch used for the molecule cross-bar latch has bipolar switching characteristics. Therefore, in order to be operated as the molecule cross-bar latch, the molecule switch must be repeatedly set and reset, which will now be described with reference to FIG. 1.
FIG. 1 is a graph showing voltage-current characteristics of a molecule switch used for a conventional molecule cross-bar latch. In FIG. 1, a first graph G1 shows an opening state of the molecule switch, that is, an OFF state, and a second graph G2 shows a closed state of the molecule switch, that is, an ON state.
Referring to FIG. 1, when a voltage greater than a set voltage Vs is applied to the molecule switch, the resistance of the molecule switch is rapidly reduced, and the voltage-current characteristic of the molecule switch follows the second graph G2. This is an ON state. Afterwards, when a voltage lower than a reset voltage Vr is applied to the molecule switch, the resistance of the molecule switch rapidly increases, and the voltage-current characteristic of the molecule switch follows the first graph G1. This is an OFF state.
When a positive (+) voltage Va smaller than the set voltage Vs is applied to the molecule switch, the molecule switch can be in an ON state or an OFF state. Thus, in order to operate the molecule cross-bar latch at the voltage Va, the set and reset operations of the molecule switch must be repeated. For example, when the molecule switch is reset, the molecule switch is in an OFF state at the voltage Va, and when the molecule switch is set, the molecule switch is in an ON state at the voltage Va. In this way, in order to operate the molecule cross-bar latch, the molecule switch must be repeatedly set and reset, thereby increasing latching time.
Second, the conventional molecule cross-bar latch uses molecules such as rotaxanes as the switching material, and thus, the molecule cross-bar latch may be weak to various physical and chemical environments that are exposed when the same is manufactured or used. Thus, the manufacture of the molecule cross-bar latch is difficult and the reliability can be hardly ensured.